The present invention generally relates to methods and devices for recording information on an optical disk based on a mark-length recording scheme, where pits are formed sequentially from the inner circumference to the outer via a light beam irradiated onto a track in the form of a groove or land running on the disk""s recording surface. More particularly, the present invention relates to an improved optical disk recording method and device which can form pits accurately on and along the center line of the optical disk track.
The present invention also relates to servo-balance adjusting methods and servo-balance detecting devices for optical disk recording and optical disk recording devices which are directed to achieving enhanced recording signal quality by optimizing servo balance in focus servo, tracking servo and the like for recording on an optical disk. More particularly, this invention relates to a technique for readily adjusting the servo balance with high accuracy.
In write-once optical disks such as CD-R (CD-Recordable) and DVD-R (DVD-Recordable) as well as rewritable optical disks such as CD-RW (CD-Rewritable), DVD-RAM and MO (Magneto Optical disk), guide grooves commonly called xe2x80x9cgroovesxe2x80x9d or xe2x80x9cpre-groovesxe2x80x9d are previously formed. Pits are formed sequentially in a track in the form of such a groove or land (a portion between adjoining grooves) by irradiating a laser light beam onto the rotating disk along the track. In recording on such optical disks, tracking control to allow the laser light beam along the track has been performed conventionally in such a way that the center of the optical axis of the laser light beam strikes the center line of the track when a tracking error signal is at a zero level.
Experiments conducted by the inventor of the present invention have shown that, in high-speed recording such as at six-times (i. e., six times faster than the normal speed), eight-times or higher speed as well as in high-density recording with a track pitch (spacing between adjoining tracks) narrower than the normal pitch, pits tend to be formed off the center line of the track even when the laser light beam is irradiated with the center of its optical axis accurately positioned at the track center line, as explained below in relation to FIG. 2.
In FIG. 2, there is shown a write-once optical disk 10 having a dye layer, where a transparent substrate 12 has grooves 14 previously formed therein and running helically around the central axis of the disk 10. Lands 16 are formed between adjoining grooves 14. The dye layer 18 functioning as a recording layer is formed on or films the transparent substrate 12, and reflective, protective and other layers (not shown for simplicity of illustration) are laminated on the dye layer 18. To record information on the optical disk 10, laser light 20, whose intensity is modulated by a recording signal, is converged via an objective lens 22 and passes through the transparent substrate 12 onto the track (groove 14 in this example), to thereby form a pit 24 therein. At that time, the tracking control is performed so as to allow the center 26 of the optical axis of the laser light beam 20 to be positioned on the center line of the track.
However, if high-speed or high-density recording is effected with such conventional tracking control, the pit 24 tends to be formed off the track center line 28 of the track T toward the inner circumference of the disk, due to the influence of residual heat from an adjoining track Txe2x80x2, located inward of the currently recorded track T, where recording has taken place immediately before the current recording. This positional deviation of the pit formed would lead to various inconveniences such as deterioration of the recording sensitivity and reproduced signal quality. Degree of the pit""s positional deviation varies depending on the type of the disk used (such as the material used for the recording layer and the track pitch) and the recording speed (linear velocity of the disk as well as a selected xe2x80x9crecording speed magnificationxe2x80x9d).
Further, in such optical disk recording, focus servo and tracking servo are each implemented by first determining a servo error through predetermined arithmetic operations between reflected light reception signals representative of a reflection of the recording laser light beam from the optical disk and then driving a servo actuator to minimize the error. In the predetermined arithmetic operations, servo-balance adjustment is made which is intended to adjust the levels of the reflected light reception signals relative to each other. The servo balance needs to be adjusted with high accuracy, because the quality and characteristics (such as a jitter characteristic) of recording signals are greatly affected depending on how the servo balance is adjusted.
FIG. 13 is explanatory of the servo balance adjustment employed in the conventional focus servo and tracking servo control (the focus servo balance adjustment is for changing the depth of the light beam focus), and more particularly showing an HF (High Frequency) signal waveform corresponding to the reflected light reception signals that represent the light beam reflection from the optical disk during recording. The HF signal waveform would present, in its falling phase, a different downward curve depending on the servo balance setting, and the sharpest downward curve generally represents an optimum servo balance setting. Thus, in plants manufacturing optical disk recording devices, it has been conventional for human operators to detect when a sharpest downward curve of the HF signal waveform appears on an oscilloscope while manipulating focus-servo-balance and tracking-servo-balance adjusting variable resistors, and fix these variable resistors at positions where the sharpest downward slope could be obtained.
However, with such conventionally servo balance adjustment, it was difficult to visually determine the sharpest downward curve of the HF signal waveform, so that the servo balance adjustment values would considerably vary depending on the human operator in charge and servo balance adjustment could not be made optimally. Automatization of the servo balance adjustment was also difficult to realize with the conventional approach. Further, an optimum focus servo balance providing an optimum focus depth of the laser beam light was not easy to achieve, since the kind and film thickness of the dye vary depending on the type of the optical disk. Similarly, an optimum tracking servo balance varies depending on the type of the optical disk. In addition, because the servo balance adjustment was already completed and fixed prior to shipment of the recording devices from the plants, the servo balance could not be adjusted freely by users depending on the type of a disk they want to use.
It is therefore a first object of the present invention to provide an optical disk recording method and device which can form pits accurately centered on the center line of a recording track.
It is a second object of the present invention to provide a servo-balance adjusting method and servo-balance detecting device for optical disk recording and an optical disk recording device which can readily adjust servo balance with high accuracy and also permit adjustment of the servo balance in actual use by users.
According to an aspect of the present invention, there is provided an optical disk recording method for recording information on an optical disk, based on a mark-length recording scheme, by forming pits sequentially from an inner circumference to an outer circumference of the optical disk via a light beam irradiated onto a track formed as a groove or land on a recording surface of the optical disk, and this optical disk recording method is characterized in that tracking control is performed in such a way that a center of an optical axis of the light beam is offset, by a predetermined amount, from a center line of the track toward the outer circumference of the optical disk. Because the tracking control is performed to cause the optical axis center of the irradiated light beam to be offset, by a predetermined amount, from the track center line toward the disk""s outer circumference, the optical disk recording method of the present invention can effectively avoid an unwanted tendency of pits being formed off the track center line toward the inner circumference of the optical disk due to the influence of residual heat from an adjoining inner track, thereby allowing pits to be formed accurately on and along the track center line.
The above-mentioned tracking control causing the light beam to be offset toward the disk""s outer circumference can be realized, for example, by appropriately setting a time period for detecting a tracking error signal to be used in the tracking control. As typically disclosed in Japanese Patent Laid-open Publication No. HEI-1-325634, the traditional tracking control for optical disk recording was performed using a tracking error signal detected only during an OFF (low-level) period of a recording pulse signal, excluding an ON (high-level) period of the recording pulse signal (i. e., a period for forming a pit with the laser light beam raised to a high recording-power level). According to such traditional tracking control, the laser light beam is controlled so that the center of its optical axis remains positioned on the center line of the track, because no influence of residual heat from an adjoining inner track appears in the tracking error signal detected during the OFF period alone. Thus, the traditional tracking control encountered the problem that pits would be formed off the track center line toward the inner circumference of the disk.
In FIG. 3, there is illustrated thermal distribution across the width of the track during optical recording thereon. The track being recorded (xe2x80x9ccurrently-recorded trackxe2x80x9d) is subject to residual heat from an adjoining inner track. FIG. 4 shows how the residual heat from the already-recorded adjoining inner track affects the currently-recorded track. If the recording is effected with the influence of the residual heat left unremoved, a portion of a pit, closer to the inner edge of the currently-recorded track, is formed more efficiently, so that a reflection from that inner portion of the pit will have a reduced light amount as denoted by a dotted-line curve in section (b) of FIG. 4. Thus, even when the optical axis of the laser light remains positioned on the center line of the track, there would be caused a significant difference in light amount between the reflection from the inner portion of the track and the reflection from the outer portion of the track as denoted by a solid-line curve in section (b) of FIG. 4, which would lead to an increased level of the tracking error signal. Note that a hatched portion in section (b) of FIG. 4 represents energy which is consumed to cause variation in the dye layer.
To avoid the inconvenience, the optical disk recording method of the present invention uses, as the time segment for detecting a tracking error signal to be used in the tracking control, a whole or part of a particular time segment within an ON period of the recording pulse signal after formation of a pit is initiated and a reflection of the light beam from the optical disk passes a peak level (the peak level is not used because of its instability), in addition to a whole or part of a time segment within an OFF period of the recording pulse signal. With the combined use of the two time segments within the ON and OFF periods, the influence of the residual heat is fed back to the tracking control to thereby produce a d.c. offset in the tracking error signal, so that the laser light beam is controlled to cause the center of its optical axis to be offset from the track center line by a predetermined amount. This arrangement can form pits centered accurately on the track. Also, according to the present invention, the length of the tracking-error-signal detecting time segment within the ON period of the recording pulse signal, for use in the tracking control, is varied depending on current recording conditions such as the type (material used for forming the recording layer, track pitch, etc.) of the optical disk and recording speed (linear velocity of the disk and selected recording speed magnification). With such variation in the time segment length, it is possible to attain an optimum offset amount corresponding to the current recording conditions, so that pits can always be formed accurately on and along the track center line, which would achieve greatly enhanced recording sensitivity and recording signal quality.
It is preferable that the tracking-error-signal detecting time segments within the ON and OFF periods of the recording pulse signal be continuous, although they may be discontinuous in some applications. By varying a start point of the tracking-error-signal detecting time segment within the ON period in accordance with the current recording conditions such as the disk type and recording speed, timing control of the tracking-error-signal detecting time segments can be greatly facilitated. Because the entire length of the tracking-error-signal detecting time segments is great as compared to the case where the tracking error signal is detected only within the OFF period of the recording pulse signal, the optical disk recording method of the present invention also can significantly increase the possibility of detecting information, such as ATIP signal, FM-recorded on wobbling portions (periodic winds or snake-like turns) of the track.
According to another aspect of the present invention, there is provided an optical disk recording device where the tracking-error-signal detecting time segments within the ON and OFF periods of the recording pulse signal are continuously interconnected, and which comprises: a tracking signal generating section that sequentially outputs a detected tracking error signal during a particular period from a given time point after formation of a pit is initiated in response to turning-on of a recording pulse signal and a reflection of the light beam from the optical disk passes a peak level to a subsequent time point when the recording pulse signal is turned on next, and that, during a period other than the particular period, either holds a level of the tracking error signal detected immediately before the particular period or outputs a zero-level tracking error signal, the tracking signal generating section smoothing the tracking error signal to thereby provide the smoothed tracking error signal as a tracking signal; and a control section that performs tracking control using the tracking signal provided by the tracking signal generating section. The optical disk recording device may also include a section for varying the start point of the tracking-error-signal detecting time segments.
The present invention also provides an optical disk recording device characterized by imparting an separately-generated offset signal to a tracking signal, in stead of expanding the tracking-error-detecting time segment. More specifically, the optical disk recording device comprises: a tracking signal generating section that sequentially outputs a detected tracking error signal during a particular period when a recording pulse signal is in an OFF state or no pit is being formed, and that, during a period other than the particular period, either holds a level of the tracking error signal detected immediately before the particular period or outputs a zero-level tracking error signal, the tracking signal generating section smoothing the tracking error signal to thereby provide the smoothed tracking error signal as a tracking signal; an offset imparting section that imparts an offset to the tracking signal; a storage section that stores information indicative of optimum offset values corresponding to various possible recording conditions such as a disk type or recording speed or a combination of the disk type and recording speed; and a control section that reads out one of the optimum offset values corresponding to current recording conditions and setting the offset, to be imparted by the offset imparting section, to the read-out offset value, and performs tracking control using the tracking signal having the offset imparted thereto.
The present invention also provides an optical disk recording device characterized by a combined use of the expansion of the tracking-error-signal detecting time segment and the impartment of the offset signal. More specifically, the optical disk recording device comprises: a tracking signal generating section that sequentially outputs a detected tracking error signal during a particular period from a given time point after formation of a pit is initiated in response to turning-on of a recording pulse signal and a reflection of the light beam from the optical disk passes a peak level to a subsequent time point when the recording pulse signal is turned on next, and that, during a period other than the particular period, either holds a level of the tracking error signal detected immediately before the particular period or outputs a zero-level tracking error signal, the tracking signal generating section smoothing the tracking error signal to thereby provide the smoothed tracking error signal as a tracking signal; an offset imparting section that imparts an offset to the tracking signal; a storage section that stores information indicative of optimum offset values corresponding to various possible recording conditions; and a control section that reads out one of the optimum offset values corresponding to current recording conditions and setting the offset, to be imparted by the offset imparting section, to the readout offset value, and performs tracking control using the tracking signal having the offset imparted thereto. In this case too, the optical disk recording device may include a section for varying the start point of the tracking-error-signal detecting time segments.
Generally, in the recording surface of recordable optical disks, there are formed, as recording tracks, guide grooves (pre-grooves) each winding or wobbling in predetermined cycles. These periodic windings are commonly known as xe2x80x9cwobblesxe2x80x9d. Experiments by the inventor of the present invention has discovered that the level of a wobble (more specifically, wobble-corresponding) component, contained in reflected light reception signals generated by receiving a reflection of the irradiated light beam from the optical disk, varies with a change of servo balance setting and that the servo balance achieving a lowest level of recording signal jitter substantially coincides with the servo balance achieving a lowest level of the wobble-corresponding component. Thus, the present invention is intended to achieve optimum servo balance adjustment on the basis of the discovered fact.
Namely, according to still another aspect of the present invention, there is provided a servo-balance adjusting method for use with an optical disk recording device for recording information by irradiating a laser light beam onto an optical disk having a track wobbling in predetermined cycles. The servo-balance adjusting method comprises the steps of: detecting a wobble component, corresponding to the frequency of the wobbles of the track, contained in reflected light reception signals generated by receiving a reflection of the laser light beam from the optical disk during recording on the optical disk; and adjusting level balance between the reflected light reception signals for use in calculation of a servo error in such a way that the wobble component detected by the step of detecting presents a substantially minimum level. Because whether or not the servo balance is optimum is ascertained on the basis of the level of the wobble component, the thus-arranged servo-balance adjusting method of the invention can adjust the servo balance in an optimum condition more readily and more accurately than the conventional approach where the servo balance condition is ascertained from the HF signal waveform.
The present invention also provides an optical disk recording device which comprises: an optical head that irradiates a recording laser light beam onto an optical disk for recording of information thereon and receives a reflection of the laser light beam from the optical disk to provide reflected light reception signals; a wobble component detecting section that detects a wobble component, corresponding to a wobble of a track on the optical disk, contained in the reflected light reception signals during the recording on the optical disk; a servo error detecting section that detects a servo error by performing arithmetic operations between the reflected light reception signals; a servo section that corrects the servo error by driving a servo actuator on the basis of the servo error detected by the servo error detecting section; an adjusting section that adjusts level balance between the reflected light reception signals to be used in the arithmetic operations performed by the servo error detecting section; and a control section that automatically adjusts the level balance between the reflected light reception signals by controlling the adjusting section in such a way that the wobble component detected by the wobble component detecting section presents a substantially minimum level.
Further, the present invention provides an optical disk recording device which comprises: an optical head that irradiates a recording laser light beam onto an optical disk for recording of information thereon and receives a reflection of the laser light beam from the optical disk to provide reflected light reception signals; a wobble component detecting section that detects a wobble component, corresponding to a wobble of a track on the optical disk, contained in the reflected light reception signals during the recording on the optical disk; a display that displays a level of the wobble component detected by the wobble component detecting section; a servo error detecting section that detects a servo error by performing arithmetic operations between the reflected light reception signals; a servo section that corrects the servo error by driving a servo actuator on the basis of the servo error detected by the servo error detecting section; an adjusting section that adjusts level balance between the reflected light reception signals to be used in the arithmetic operations performed by the servo error detecting section; and a level balance adjusting operator that is operable to manually adjust the level balance between the reflected light reception signals by controlling the adjusting section in such a way that the wobble component detected by the wobble component detecting section presents a substantially minimum level.
With the two optical disk recording devices arranged in the above-mentioned manner, the servo balance adjustment can be made as desired by users depending on the type of an optical disk they want to use. It will be appreciated that the optical disk recording device of the present invention may comprise an optical disk drive operating singly or in combination with a personal computer. In the latter case, the optical disk drive may include a level balance adjusting circuit and a level balance adjusting operator, while the personal computer may includes a control circuit and a display.
Moreover, the present invention provides a servo balance detecting device suitable for use with an optical disk recording device which is not itself equipped with facilities necessary for servo balance adjustment. Namely, this servo balance detecting device comprises: an input terminal section that receives reflected light reception signals corresponding to a reflection of a recording laser light beam irradiated by an optical disk recording device onto an optical disk; a wobble component detecting section that detects a wobble component, corresponding to a wobble of a track on the optical disk, contained in the reflected light reception signals received via the input terminal section; and a display that displays a level of the wobble component detected by the wobble component detecting section.
As will be apparent from the following description, the present invention arranged as above is applicable to servo balance adjustment in optical disk recording devices for various types of optical disk, such as CD-R, CD-RW, DVD-R, DVD-RAM and MO.